1. Technical Field
The present invention relates to a recording method of performing recording on a recording medium by operating a recording unit, such as a recording head, for scanning, such as a lateral type recording method or a serial type recording method, and a recording apparatus.
2. Related Art
For example, a printing apparatus (recording apparatus), such as a lateral scan type printer or a serial type printer, prints a document or an image on a recording medium (target) by spraying ink droplets from the nozzles of a recording head disposed on a carriage during each of movement while moving the carriage several times (several passes) in the main scanning direction. A nozzle line, in which a plurality of nozzles (for example, 180 or 360) is arranged at regular pitches in a sub-scanning direction crossing the main scanning direction, is formed for each color on a nozzle-forming surface opposite to the target of the recording head.
The gap of dot lines (raster lines) in the sub-scanning direction, which are drawn by the nozzles in lines in the main scanning direction when the carriage performs main scanning, depends on the variation in the nozzle pitch. For example, in band printing that performs printing by using all of nozzles, the variation in the pitch of the nozzles is reflected as the variation in the gaps of the raster lines, such that banding (concentration non-uniformity), such as white stripes extending in the main scanning direction, is generated on a printed image, which causes reduction in print quality. This is because the nozzles used for drawing adjacent raster lines are always the same adjacent nozzles. Therefore, an interlaced recording method (microweave recording method) that selects nozzles that are not adjacent to each other and used for drawing adjacent raster line may be employed particularly in a print mode for printing a high-quality print image.
A print image is formed in the interlaced recording method by drawing a plurality of raster lines in first main scanning (pass) of a carriage with a predetermined number of nozzles in the sub-scanning direction as used nozzles in all of nozzles in a nozzle line, moving the carriage to the next pass position in the sub-scanning direction, drawing raster lines to fill the gaps between the previous pixel lines by using the used nozzles in the next pass, and gradually filling the gaps with raster lines by repeating this operation several times.
For example, JP-A-2010-253699 discloses a technology of acquiring a correction value for correcting a gradation value of a line region corresponding to a nozzle on the basis of a read-out gradation value, which is acquired by printing a correction pattern and reading out the pattern with a scanner, in order to reduce banding.
However, when images for a label are continuously printed on a long recording medium, such as rolled paper in the lateral scan type, a carriage (recording head) performs main scanning in the transport direction of the recording medium, such that printing is performed by a predetermined length in the longitudinal direction of the recording medium. Therefore, the boundary between the previous printing and the next printing of the recording head may be generated in one image. In this case, there is a problem in that banding, such as a white stripe extending in the sub-scanning direction, occurs around the boundary of the previous printing and the next printing in the image. The technology disclosed in JP-A-2010-253699 initially sets a correction value for correcting a gradation value in a printing apparatus during product shipping or the like, such that it is difficult to remove banding that extends in the sub-scanning direction and may occur at the boundary of the previous printing and the present printing even by using the technology of JP-A-2010-253699.
Further, when printing is performed on a transparent recording medium, such as a transparent film, a double-plate printing, which prints (basic printing) a base plate image (for example, beta print image) with a basic color (for example, white) ink and then printing a plate of a main image over the basic plate image (main printing), is performed. In this case, since the basic ink is difficult to dry, the ink for main printing performed over the half-dried basic print image soaks, such that the print quality is deteriorated. In order to solve the problem, for example, it is possible to consider a recording method that performs basic printing on the upstream half of a print area and performs main printing on the downstream half in main scanning, transporting a recording medium by half the length of the print area in the main scanning direction each time one lateral scanning is finished by finishing main scanning a predetermined number of times in the interlaced recording method, and thereafter alternately repeating these operations. According to this recording method, only the time in which the time interval from the previous basic printing to the present main printing is the same as the time taken for one lateral scanning is ensured. Therefore, it is possible to avoid deterioration of print quality due to main scanning being performed after basic printing with dried ink and the ink for the main printing soaks. However, banding that extends in the sub-scanning direction due to boundaries in a print image occurs in the recording method, when the boundary between the previous basic printing and the present basic printing and a boundary between the previous main printing and the present main printing are in the image range.
On the other hand, a time interval for avoiding the soaking is disclosed, for example, in JP-A-2000-229425, in which the time T (ms) that is necessary until ink droplets completely permeate the recording medium is expressed by T=(4V/πD2Ka)2. In the expression, V is the maximum amount of ink droplets (ml) discharged from an ink jet head by one operation, D is an average equivalent circle diameter (m) of the dots when the ink droplets are landed on the recording medium, and Ka is an absorption coefficient (ml/m2·ms1/2) for ink to permeate the recording medium. In JP-A-2000-229425, when the time until the next ink droplets are landed on the same position after ink droplets are landed on a recoding medium is Tx (ms), the conditions of T, V, D, and Ka are set to satisfy T≦Tx, that is, (4V/πD2Ka)2≦Tx. However, when the type of ink, the material of the recording medium, the maximum amount of ink droplets, or the average equivalent circle diameter D of the dots is usually determined in advance by a user and V, D, and Ka are hardly be changed in this case, such that it is necessary to ensure a time interval equal to or more than the time T=(4V/πD2Ka)2 that is determined from V, D, Ka according to the type of ink or the material of the recording medium. In particular, since it is difficult to dry or cure ink containing aqueous resin (aqueous resin ink) in comparison to ECO-SOL ink (a kind of organic solvent ink) or ultraviolet-curable ink (UV ink), it is necessary to lengthen the time after ink droplets are landed on the recording medium until the next ink droplets are landed on the same position.
An advantage of some aspects of the invention is to provide a recording method and a recording apparatus that can reduce banding (concentration non-uniformity) that extends in a sub-scanning direction in a recording method of moving a recording unit for scanning.